1. Field of the Invention
The present invention relates to a rotating apparatus which is used in a light deflecting apparatus for use in a laser beam printer or the like.
2. Related Background Art
In recent years, there has been an increasing demand regarding a rotating apparatus to rotate at a high speed or a high accuracy increasing. Particularly, in a light deflecting apparatus which is used in a laser beam printer, a dynamic pressure bearing which rotates in a contactless manner is used to obtain a high accuracy rotating apparatus. FIG. 1 shows a deflection scanning rotating apparatus of a laser beam printer using a dynamic pressure bearing. A rotary shaft 1 is rotatably fitted into a sleeve 2. A thrust plate 3 is arranged together with a fixed plate 4 to a lower edge portion of the sleeve 2 and fixed to an outer cylinder 5.
A flange 6 is fixed to the rotary shaft 1. A rotary polygon mirror 7 to deflect a light flux is fixed to an upper portion of the flange 6. A yoke 9 in which a driving magnet 8 is fixed to the inner peripheral surface is fixed to a lower portion of the flange 6. A stator 10 is fixed to the outer cylinder 5 arranged at a position where it faces the driving magnet 8. A shallow groove 11 is formed on the surface of the thrust plate 3 at a position which faces an edge portion of the rotary shaft 1, thereby forming a dynamic pressure thrust bearing. A hole 12 and a groove 13 to circulate a lubricating fluid are also formed. A herringbone-shaped shallow groove 14 is formed on an outer peripheral surface of the rotary shaft 1 at a position which faces an inner peripheral surface of the sleeve 2, thereby forming a dynamic pressure radial bearing. Further, a spiral shallow groove 15 is formed near the sleeve opening portion so as to allow the lubricating fluid to flow in the dynamic thrust bearing. A concave portion 16 is formed in the sleeve 2 at a position between the herringbone shallow groove 14 and the spiral shallow groove 15 and a small diameter hole 17 is also formed, thereby assuring the stability of the dynamic pressure bearing using a fluid (oil, grease, or the like) as a lubricating fluid.
However, the above conventional apparatus has the following drawbacks in order to assure the stable dynamic pressure bearing. That is, after the dynamic pressure bearing has been assembled, when a shock or the like acts on the rotary polygon mirror as a rotary member, the rotary member is lifted up and air is mixed into the lubricating agent (oil, grease, or the like). Thus, there is a case where the stable characteristics as a dynamic pressure bearing rotating apparatus cannot be obtained. On the other hand, when the rotary member is unexpectedly lifted up, the rotary member is pulled out of the fixed member. Therefore, a handling performance of the dynamic pressure bearing after completion of assembly is troublesome.